Also Known As
Undescended Testicle, Retained Testicle, Rig, Ridgling
Cryptorchidism means, "hidden testes" (crypt = hidden, orchid = testes). This term describes the condition in which one or both testicles do not descend normally into the scrotum of the horse. When one or both testicles are not descended in the scrotum, the horse may also be referred to as a rig, ridgling as well as a cryptorchid. Cryptorchidism is a developmental defect in both animals and humans.
Horses with one descended testicle are usually fertile, while horses with both undescended testicle are generally sterile. The testes may be retained anywhere from the abdomen to the inguinal canal, the normal passage route into the scrotum.
Three different forms of cryptorchidism are observed in horses: under the skin in the inguinal area, in the inguinal canal and in the abdomen. In bilateral cryptorchids, most of the time both testes are abdominal.
Prevalence of left and right testicular retention is nearly equal, although retained left testes are more often in the abdomen while the right retained testicle is more often in the inguinal canal. All breeds of horses may be exhibit cryptorchidism, but there is ahigher frequency in Quarter Horses, Saddlebreds, Percherons, and ponies. Many breed associations do not allow registration of cryptorchids,
Cryptorchidism is considered inheritable, so affected horses should be castrated to help prevent continuation of this congenital defect and for safety reasons since undescended testicles lead to characteristic stallion behavior
Horse with both or bilateral undescended testes
- Physical appearance of a gelding and testes cannot be palpated
- Stallion-like behavior
Horses with one or unilateral undescended testicle
- One testicle remains in abdomen
- Horse is fertile from the one descended testicle
A single cause of equine cryptorchidism has not been established and contributing causes are currently undetermined. The condition is likely the result of a complex combination of genetic, hormonal, and mechanical factors.
Because the exact causes of cryptorchidism are unknown, little can be done to prevent the condition. Because the condition appears to be genetic, most veterinarians advise against using cryptorchids for breeding purposes.
Medical treatment to stimulate descent of retained testes in horses is controversial in regards to both effectiveness and ethical considerations. Although sporadic anecdotal reports suggest that hormone administration may have aided in testicular descent in some horses, the majority opinion is that medical treatment is not effective.
In addition, many owners, breeders and veterinarians are of the strong opinion that cryptorchidism may be inherited and that medical or surgical procedures intended to induce or aid testicular descent should not be performed
Until recently, the only surgical technique described for removal of retained testes was laparotomy under general anesthesia. Recently, laparoscopy under general anesthesia and laparoscopy while standing have been used to treat cryptorchidism in horses.
Laparotomy is the surgical opening of the abdomen under general anesthesia by a number of surgical approaches including an inguinal approach with or without retrieval of the inguinal extension of the gubernaculum testis, a parainguinal approach (to the side of the inguinal ring), or, less commonly, a flank approach.
The inguinal and parainguinal approaches involve the incising of the skin, and blunt dissection down to the inguinal ring. The vaginal process, epididymis and/or scrotal ligament will be identified, the vaginal process opened, and the retained testis exteriorized and emasculated. If these structures are not identified, deeper dissection will be required.
Special attention to the closure of the incision will be required since the intestine can eviscerate through the open vaginal process.
Laparoscopy is an endoscopic procedure where a small, fiber-optic, video camera and surgical instruments are introduced into the abdomen through a small incision. This permits the observation of the inside of the abdomen and allows for the performance of abdominal surgeries without a large incision into the abdominal cavity.
The main advantages are the small incisions, minimal postoperative pain and the fact that the horse can return to exercise very quickly. Laparoscopy can be used to remove retained abdominal testes in horses. Depending on the horse's temperament and on the surgeon's preference, the laparoscopic surgery will be performed in a standing position or laying down under general anesthesia.
Standing laparoscopy is performed under local anesthesia and tranquilization with the horse restrained in a set of stocks. It is relatively painless and minimally invasive.
After sedation of the horse, local anesthetics are injected to deaden nerve sensation to the flank area and three 1-cm incisions are made through the muscle layers of the flank into the abdominal cavity. These incisions are for the insertion of the laparoscopic camera and surgical instruments.
During the procedure, carbon dioxide gas is used to inflate the abdominal cavity to allow for better visualization. Under laparoscopic guidance, the testis is ligated, emasculated and removed.
General anesthesia laparoscopy involves the administration of general anesthesia and placing the horse on its back. Once an adequate plain of anesthesia is reached, small incisions are made in the abdominal wall. As in the standing laparoscopic procedure, the abdomen is inflated and the retained testis located and removed.
The small incisions are closed and the horse recovered from anesthesia. Both laparoscopic methods involve minimal invasion and pain but require more extensive equipment and specialized training to perform than open surgical procedures.
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